The present invention relates to laser catheters and, more particularly, to a laser catheter for removing athereosclerotic plaque.
The use of laser catheters for removing obstructions from blood vessels and the like is known, generally. However, these catheters employ standard visable light lasers which have a number of disadvantages when used within blood vessels. More particularly, when such a standard visible laser is used, the material being destroyed is heated to vaporization/combustion. Because the targeted material is heated to such an extent in order to be destroyed, healthy tissue surrounding the targeted tissue is also heated and can be charred and/or otherwise loose its structural integrity. Further, because it is difficult to control the direction of the laser beam of standard visible lasers within the vessel, perforation of the blood vessel wall is likely.
There have been attempts at controlling the direction in which the laser beam is emitted and hence the material impinged thereby. However, these attempts have primarily lead to providing catheters wherein the laser beam is directed radially of the vessel to impinge upon a particular targeted portion of the athereosclerotic plaque. Directing the laser beam towards the side wall of the blood vessel, however, can easily lead to perforation of the blood vessel and/or weakening of the vessel wall due to the excessive heating of the healthy tissue forming the wall.
Other attempts have also been made, such as injecting luminescent dyes into the blood stream in order to more readily recognize the targeted portion of the vessel and to thereby minimize the likelihood of damaging healthy tissue. However, the heat of the laser will still cause damage to the healthy tissue.
Thus, while the use of lasers within blood vessels initially appeared to be promising, doctors and researchers have become discouraged at the uncontrollability of currently available visable light laser catheters. Indeed, even when a standard visible laser is used, for example, during open heart surgery it has been found that there is often rapid restenosis of the targeted portions of the vessel and, despite greater accuracy in terms of targeting the laser, the exposure of healthy tissue to excessive heat still leads to deleterious results.
Another attempt at controlling lasers applied to blood vessels is known as the excimer laser which is a combination of argon fluoride or krypton chloride and a rare earth gas. This combination forms a laser beam having a very short wavelength and hence photons of very high energy. Thus, the excimer laser enables the disintegration of targeted tissue before the vaporization stage and can yield relatively pure disintegration without excessive thermal damage to otherwise healthy tissue.
While the thermal damage is reduced with the excimer laser, there is still a great deal of heat transmitted which can destroy enzymes and the like in the surrounding tissue. Further, because the excimer laser utilizes far ultraviolet rays, questions have been raised as to whether this device will increase the risk of cancerous tissue development. Finally, the photon energy of the excimer laser is so high that it is very difficult if not impossible to transmit the laser effectively through known fibers.